I am not sure what you mean by “persistent” and yes, those “symlink” will have to be read by a TChain, together with other trees (in different files) with the same name but not using the “symlink” system
I thought about creating friends with only a single branch copied from the original tree but then the additional trees do not have the exact same structure (in terms of branch read directly from them or from the original tree) than the original and ROOT gets confused when both types are read at the same time e.g. in a TChain (see Behavior of TChain when adding Trees which have friends already defined)
I thought about using the TreeFriend system (which in general is very useful) but the issue is summarised above, ultimately I would like to include all three variations I need in a single TChain (using a single tree name) and only the “nominal” tree will include this friend system so the TChain will get confused, as reported in the thread mentioned above.
Maybe actually the easiest way would be to fix the weird TChain behavior? If you think so I can work on a reproducible example next week.